Permafrost in monitored unstable rock slopes in Norway – new insights from temperature and surface velocity measurements, geophysical surveying, and ground temperature modelling

• Published in: Earth surface dynamics Vol. 10; no. 1; pp. 97 - 129
• Main Authors: Etzelmüller, Bernd, Czekirda, Justyna, Magnin, Florence, Duvillard, Pierre-Allain, Ravanel, Ludovic, Malet, Emanuelle, Aspaas, Andreas, Kristensen, Lene, Skrede, Ingrid, Majala, Gudrun D, Jacobs, Benjamin, Leinauer, Johannes, Hauck, Christian, Hilbich, Christin, Böhme, Martina, Hermanns, Reginald, Eriksen, Harald Ã, Lauknes, Tom Rune, Krautblatter, Michael, Westermann, Sebastian
• Format: Journal Article
• Language: English
• Published: Gottingen Copernicus GmbH 01-02-2022; Copernicus Publications; European Geosciences Union
• Subjects: Deformation; Degradation; Displacement; Electrical resistivity; Environmental Sciences; Failure; Fractures; Geological surveys; Geophysical methods; Geophysics; Global navigation satellite system; Ground ice; Hydrostatic pressure; Interferometric synthetic aperture radar; Melting point; Melting points; Modelling; Mountains; Navigation; Navigational satellites; Permafrost; Plateaus; Precipitation; Prospecting; Rocks; Rockslides; SAR (radar); Seasonal variations; Seasonality; Shear strength; Slope; Slope stability; Slopes; Snowmelt; Soundings; Surface temperature; Surface velocity; Surveying; Thermal analysis; Time series; Tomography; Two dimensional models; Water pressure; Norway
• ISSN: 2196-632X; 2196-6311; 2196-632X
• DOI: 10.5194/esurf-10-97-2022

The warming and subsequent degradation of mountain permafrost within alpine
areas represent an important process influencing the stability of steep slopes and
rock faces. The unstable and monitored slopes of Mannen (Møre and Romsdal
county, southern Norway) and Gámanjunni-3 (Troms and Finnmark county,
northern Norway) were classified as high-risk sites by the Norwegian
Geological Survey (NGU). Failure initiation has been suggested to be linked
to permafrost degradation, but the detailed permafrost distribution at the
sites is unknown. Rock wall (RW) temperature loggers at both sites have
measured the thermal regime since 2015, showing mean rock surface
temperatures between 2.5 and −1.6 ∘C depending on
site and topographic aspect. Between 2016 and 2019 we conducted 2D and 3D
electrical resistivity tomography (ERT) surveys on the plateau and directly
within the rock wall back scarp of the unstable slopes at both sites. In
combination with geophysical laboratory analysis of rock wall samples from
both sites, the ERT soundings indicate widespread permafrost areas,
especially at Gámanjunni-3. Finally, we conducted 2D thermal modelling
to evaluate the potential thermal regime, along with an analysis of
available displacement rate measurements based on Global Navigation
Satellite System (GNSS) and ground- and satellite-based interferometric
synthetic aperture radar (InSAR) methods. Surface air and ground
temperatures have increased significantly since ca. 1900 by 1
and 1.5 ∘C, and the highest temperatures have been measured and modelled
since 2000 at both study sites. We observed a seasonality of displacement,
with increasing velocities during late winter and early spring and the highest
velocities in June, probably related to water pressure variations during
snowmelt. The displacement rates of Gámanjunni-3 rockslide co-vary with
subsurface resistivity and modelled ground temperature. Increased
displacement rates seem to be associated with sub-zero ground temperatures
and higher ground resistivity. This might be related to the presence of
ground ice in fractures and pores close to the melting point, facilitating
increased deformation. The study demonstrates and discusses the possible
influence of permafrost, at least locally, on the dynamics of large rock
slope instabilities.